How do I make charcoal that achieves biochar structure and chemistry?
Structure is a mostly of a function of the fuel type. Hardwoods are currently preferred in this regard, but the understanding in this area is in flux. The chemistry is better defined. The burn process should be controlled to retain condensates. The tools to achieve this in a home-based setting are limited but also blessedly simple. In all approaches it means restricting the air supply to slow the burn rate and achieve a low enough pyrolysis temperature that all the tars and volatiles produced don’t gas off. Being willing to tolerate the inefficent combustion of smoke production, even if only near the end of the burn, certainly makes it easier to retain this volatile liquid component. Being willing to dowse or damping off the burn before it makes the transition from a wood gas fire to a coal gas fire also helps. That can result in some brown char mixed in with the black char, but when it comes to garden soil, its all good.
